Optimal stride

What makes an optimal stride? It seems that nobody knows for sure. According to Kevin Beck of Human Kinetics, Inc of Champaign, Illinois: "It would be great to answer that question, but in fact, no one knows."

As a general rule, taller runners with longer legs have longer optimal strides. On average their optimal strides are 1.4 times their leg length (while running seven minute miles). However, on an individual basis, height and leg length are poor determinants of optimal stride.

In a study of 10 experienced runners, the subject with the shortest leg length had the longest self-selected and the longest optimal stride. The runners, on average, chose strides just four centimeters from optimal.

Beck adds that "most experienced runners select a stride length that does not differ dramatically from the ideal". This implies that overall running experience has something to do with the capacity to self-select an optimal length of stride.

In one study, when collegiate runners were studied from the beginning to the end of their competitive careers, researchers found that running stride lengths tended to decrease from their first year to their final year. This is in line with the findings that elite runners tend to have shorter strides than experienced but less accomplished runners.

But does all of this help an individual runner to optimise his or her stride? After all, some runners self-select strides that are shorter than optimal.

Beck further adds that "without true predictors of what an optimal stride length is for an individual (and even a trained coach would probably have a hard time determining whether a runner was over-striding or under-striding), there's not much a runner can do except let his or her body adjust to an optimal stride through experience".

It is possible that runners choose a stride rate that is most efficient, regardless of the speed, and adjust stride length to obtain the desired speed.

According to Beck, "this is because stride length has to balance with stride frequency, or stride rate, to produce a given speed, and because each runner's stride length varies widely across speeds while stride rate stays relatively constant - increasing slightly with increasing speeds.

Optimal speed

Humans adjust their walking and running gaits to minimise the metabolic energy cost of motion. The walking speed that we tend to prefer is the one that minimises energy cost per unit distance.

According to Dr R McNeill Alexander of the School of Biology at the University of Leeds, writing in the September 2002 issue of the American Journal of Human Biology: "When time is valuable, faster speeds might seem preferable. At speeds up to two metres per second, walking requires less energy than running, and we walk. At higher speeds, running is more economical, and we run. At each speed we use the stride that minimises energy costs."

From the use of a computer model that predicts metabolic rates for all conceivable gaits of a simple biped, we understand these and other features of human gait. For example, the energy cost of walking is increased on uphill slopes and also on soft ground such as sand. Energy expended is greater with an increased heavy load as well.

Interesting facts

Humans may be the most efficient of all animals at one type of running: Trotting. We may not be the fastest runners over a short distance, but we trot the best over long distances. Humans often survived by wounding a large game animal during a hunt and tracking it down often over great distances until it fell. We did this thanks to our ability to trot.

Humans have been walking as we do today for about 3.2m years. This is according to research headed by Dr William Sellars from the Department of Human Sciences at Loughborough University in the UK and published in the July 2005 Interface of the Journal of the Royal Society.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au